"20/20" continues, with David Muir. Reporter: Tonight, the counterfeit goods in every corner of your home. The smartphones, the bike helmets, the toothpaste, the make-up, and the suburban family about to be stunned by their airbag and our test. We're about to uncover it all. We go in at level ten. Do you have any weapons on you? Reporter: Nine months after we first began our investigation, "20/20" is back in Los Angeles. We wanted to know, are those alleged counterfeit dealers, first arrested as our cameras were rolling, already back on the streets? Just listen to the lead investigator describe who they're after now. She has a push cart and she's sold counterfeit pharmaceutical drugs. Reporter: A push cart. A tiny little mobile pharmacy. Sound familiar? She's wearing a red and gray striped shirt with a gray sweatpants. Reporter: She is right outside the market. That's her little van right there. Reporter: Where did she get her hands on it? Normally like El Salvador, Guatemala. Reporter: Is any route like that legal in the United States? No. Reporter: And soon we're off. Several cars. One undercover agent will make the buy. She's right there. Reporter: We park about 100 feet away. An investigator tells us the woman went to re-stock. We wait. Roger, I should see her any second now. Okay, she is right in front of us. She is pushing two boxes, fruit boxes. Reporter: And look at this tonight. They gave "20/20" the undercover video from the LAPD, showing the moment that they say the undercover agent buys suspected counterfeit antibiotics from that woman on the street. The buy's been made. Let's do it. Reporter: We head in. Across the parking lot. 4 Ida 20. Can you please show me code 6? Reporter: She's gone. She's actually going northbound on Kenmore. Stay here. Yeah, she's with me. Reporter: Investigators say she was trying to slip away to her apartment not far away. Explain to her that we just saw her go back over there, enter the courtyard in the back of the storage unit. I saw you. We have cameras. No. Reporter: Investigators say they find the bag. The medicine that they believe she wheeled right in front of us. A blue bag full of prescription drugs. Most of it they believe is counterfeit medication. What is this? Terramycin, optomic ointment. Reporter: It says pfizer. Right, exactly. So, usually this comes from central America that they import up here. Reporter: So this is not an approved pfizer manufactured drug here in America? Right, exactly. Yes. And you don't know what kind of standards they've done to actually make or manufacture this down in central America. Reporter: And yet, people are buying it on the street for how much? This is going for about 40 to 50 dollars. Reporter: And he shows us the potential danger. Break away from you, and see how it breaks, it's not even --. And shards of glass can always get inside. We're not even quite sure if this is a true manufactured medication. Reporter: So, this is a prescription anti-inflammatory you'd buy for arthritis. Correct. You can get this and walk right around the corner and inject yourself. Reporter: I ask her, is she worried at all about her customers? No. Reporter: I ask, are you worried about the medicine? Silence. And if you are feeling at all badly for her, investigators say she's likely part of something much larger. They believe foreign counterfeiters are supplying her. And I ask, how much money does she make in a week? She said 800 a week. That's a lie, that's a lie. Reporter: How much do you think? Over $1,000 a week. No problem. No problem at all. That's more than most Americans make. Reporter: Suddenly we notice two men approaching. David, you want to come over here? Reporter: Sure. Two men who have purchased medicine here before, are now back, angry over what they say it did to them. He shows us where he had the pain after taking the medication. You can hear him saying it's "ABC." And he pulls his shirt down. It's ABC, I don't want to be on ABC. Reporter: But we tell him, we're here to uncover the possible dangers of counterfeit medicine, and he decides to keep talking. Yeah, I got an injection from her, for the brain. Expired, it was expired. Reporter: He says his friend got an infection. Reporter: We ask this man who told us to blur his face, what kind of medicine he took. What kind of -- what type of injection? Yeah. It was a vitamin -- vitamin shot. Reporter: And we ask the obvious question. Why buy drugs on the street? They're made from Merrick. Reporter: And we tell one of the investigators, the pharmacist, that he thought the medicine was from Merck. You heard him tell us that the drug was from Merck. That's how he knew it was okay. And it's not, it's not the Merck that you're thinking. It's counterfeit. Reporter: Investigators are now checking out the garage behind the grocery store. You can see children on the street watching all this unfold, but right over my shoulder, is the supermarket here in this central Los Angeles neighborhood and they are convinced that back here in one of the garages she has essentially a supply of this medicine that she is selling on the streets. Go ahead, open it. Reporter: So I ask, why sell in the streets? Reporter: She has no answer. Then there's the heat. Well into the 90s, on the day we were there. She thinks it's okay in the heat. Yeah, she says it's hot. Reporter: What temperature should this be stored at? It's got to be somewhere between 60 and 75 degrees. If there is antibiotic inside, you may not be getting anything in there because it's all been denatured by the sun. Reporter: Essentially baked out of it. Right. Reporter: And along with all that medicine -- the cash. This is just from today. I mean, that's a lot for two hours of work. Reporter: Customers are drawn to her because much of the medicine is inexpensive. A lot of people are going to look at her and say, "Do you feel sorry for her?" You know, I totally understand what people think in perception. But because she's older, a lot of these folks down here feel safe to approach her to buy these. Reporter: You think it's a trust thing. It's a trust, absolutely. Reporter: When we come back tonight, our producers are out all across America with prescriptions from their own doctors. Those storefronts promising cheaper medicine with Canada in the name. But did any of the drugs we ordered actually come from Canada? And once they arrived, would they past the test? And later tonight, the counterfeit goods in every corner of your home. The toothpaste. Had antifreeze. Reporter: The airbag we put to the test. And the makeup. What are you really putting on your face?

This transcript has been automatically generated and may not be 100% accurate.

Now Playing: What the fascinator?! Why guests at the royal wedding wear hats

Now Playing: Pilots who safely landed Southwest flight remember moment they knew there was trouble

Now Playing: Pilots who safely landed Southwest flight on their bond and their lessons for pilots

Now Playing: What pilots who safely landed deadly Southwest flight may have experienced in cockpit

Now Playing: Pilots, passengers of deadly Southwest flight on the life-changing ordeal: Part 6

Now Playing: Southwest passengers prepare for the worst after blown engine, smashed window: Part 3

Now Playing: {{itm.title}}

{"id":31088958,"title":"Police Confront Woman Selling Alleged Counterfeit Drugs on the Street","duration":"6:50","description":"Part 2: A man who purchased medicine from the woman said his friend got an infection from the drug.","url":"/2020/video/police-confront-woman-selling-alleged-counterfeit-drugs-street-31088958","section":"2020","mediaType":"default"}